Traditional soap bars are made from soap noodles, with 70 wt % or more of total fatty material (TFM), 10-14 wt % water, and include other additives (such as titanium dioxide, surfactant and fragrance). These bars are mainly produced by mixing the soap noodles with other additives, followed by milling, extruding and stamping processes.
Generally, traditional soaps are alkali (usually sodium) salts of fatty acids from oils or fats, which can come be of animal and/or plant origin. Common sources of oils and fats are, for example, palm oil, palm kernel oil, coconut oil, cattle tallow, sheep tallow, lard, and other similar oils and fats from other organisms. Fats and oils contain in substantial part glycerides of varying chain lengths, which are esters of glycerol (glycerin) and fatty acids. Under alkaline conditions and heat, the glycerides in the fats and oils form glycerin and fatty acid salts, also known as soaps.
Commercially, soaps are made by adding additives to soap noodles and further processing the mixture into soap. Soap noodles are typically made from oil or fat of blends thereof by three methods commonly known in the art. One method is the direct saponification of oil/fat in which the oil/fat is reacted with an alkali (typically sodium hydroxide) to form glycerin and the soap base (which contains fatty acid alkali salt, e.g., fatty acid sodium salt, which is also carboxylic acid sodium salt). The soap base is the fatty-acid-alkali-salt-containing material that is to be used for forming soap by adding fillers, fragrance, and other additives. Thus, the material after removal of glycerin (if glycerin is to be removed) and to be further processed is an example of soap base. Another method of making soap involves the neutralization of fatty acid with the alkali (e.g., NaOH) to form the soap base. In the soap-making process, the soap base can be dried and plodded into noodles or chips. As used herein, the term “soap noodles” refers to the pellets or pieces of soap (whether they be in pellet, chip, bits, or other shapes). Soap noodles are typically the result of the drying and extruding of raw soap into unit form such that the soap units or pieces can be further processed into the finished soap bars by mixing with additives, as known to those skilled in the art of soap making. The soap noodle contains the soap base and can optionally contain other materials such as glycerin. Cleansing soap bars are mostly produced by mixing the soap noodles with additives, such as fragrance, fillers, etc., followed by milling, extruding and stamping processes.
Traditionally, finished milled soap bars include soap noodle TFM of more than 70 wt %, 10-14 wt % water, and other additives (such as titanium dioxide, surfactant and fragrance). At the present, milled bars generally have a water content of about 8-15 wt % and hard non-milled bars have a water content of about 20-35 wt %. Hard non-milled bars can contain moisture of less than 35 wt %. Such non-milled bars have a TFM of about 30-65 wt %. The reduction in TFM traditionally is done by including insoluble particulate materials and/or soluble silicates in the soap bars. Such non-milled bars are generally quite soft and subjecting the soap bars to the milling process will cause water to separate out.
Generally, fillers are used as soap noodle replacement in soap formulation design. For example, commonly used fillers include kaolin, talc and other inorganic mineral fillers. More than 16 wt % of kaolin can be used in the soap formulation with the acceptable properties and kaolin might reduce the feeling of greasiness on the skin. Other materials that have been added in the making of soap include silica gel, sodium aluminate, and borate compounds. In some cases, water absorbing materials are added in soap-making to increase the content of water. Examples of patent documents related to soaps that have water absorbing material include US 20050276828A and WO2007146027. Examples of patent documents that are related to adding fillers or including water absorbing material in the soap making process include U.S. Pat. Nos. 2,677,665, 5,703,026, 6,310,016, 6,440,908, and 7,285,521.
However, the inclusion of a large amount of water or fillers into the soap bar not only may affect the cleansing and sensory feel of the soap, but often also adversely affect the processing conditions. There continues to be a need for improved soap bars with an increased amount of water or fillers wherein the soap bars are able to provide effective cleansing property with lowered TFM.